docs: def add_distdiff_optgroup(parser):
      """
      Option group relating to the use of a DistChange or DistReport
      """
  
      # for the --processes default
      cpus = cpu_count()
  
      og = parser.add_argument_group("Distribution Checking Options")
  
      og.add_argument("--processes", type=int, default=cpus,
                      help="Number of child processes to spawn to handle"
                      " sub-reports. Set to 0 to disable multi-processing."
                      " Defaults to the number of CPUs (%r)" % cpus)
  
      og.add_argument("--shallow", action="store_true", default=False,
                      help="Check only that the files of this dist have"
                      "changed, do not infer the meaning")
  
      og.add_argument("--ignore-filenames", action="append", default=[],
                      help="file glob to ignore. Can be specified multiple"
                      " times")
  
      og.add_argument("--ignore-trailing-whitespace",
                      action="store_true", default=False,
                      help="ignore trailing whitespace when comparing text"
                      " files")